65-70 days. The Parris Island Cos lettuce is a Romaine lettuce, which means it is among the most nutritious of lettuce varieties. These non-GMO seeds grow upright into tall heads of lettuce that are ready to harvest in 65 to 70 days. The Parris Island Cos is resistant to mosaic virus, and the leaves have a mildly sweet flavor. Midribs are crunchy and juicy. Because of their higher chlorophyll content, romaine lettuces are among the most nutritious of all lettuces. Excellent performer in the intermountain region. Mosaic tolerant.